Low cost design of parallel parking assist system based on an ultrasonic sensor

International Journal of Automotive Technology, Vol. 11,  No. 3, pp. 409−416 (2010) DOI 10.1007/s12239−010−0050−0

Copyright © 2010 KSAE 1229−9138/2010/052−14

LOW COST DESIGN OF PARALLEL PARKING ASSIST SYSTEM BASED ON AN ULTRASONIC SENSOR

  S. H. JEONG1)*, C. G. CHOI1), J. N. OH1), P. J. YOON1), B. S. KIM2), M. KIM2) and K. H. LEE2)

1)MANDO Central R&D Center, 413-5 Gomae-dong, Giheung-gu, Gyeonggi 449-901, Korea 2)School of Electronic Engineering, Sogang University, Seoul 121-742, Korea

(Received 5 August 2008; Revised 7 December 2009)

ABSTRACT−This paper presents a low cost design and implementation of a parallel parking assist system (PPAS) based on ultrasonic sensors. Generally, a PPAS requires several types of sensors, such as an ultrasonic sensor, camera sensor, radar sensor and laser sensor for parking space detection. However, our proposed PPAS only requires two ultrasonic sensors on the front and lateral sides for parking space detection. Moreover, a steering angle sensor and wheel speed sensor installed in the vehicle are used to obtain vehicle position information for localization in ultrasonic range data. The hardware architecture of the PPAS based on an electronic control unit (ECU) module, sensor modules and a human machine interface (HMI) module was proposed. Moreover, the software architecture of the PPAS is based on system initialization, scheduling, recognition and a control algorithm. In particular, a novel sensor algorithm was proposed to minimize the vehicle corner error of the ultrasonic sensor. A prototype of the PPAS based on the proposed architecture was constructed. The experimental results demonstrate that the implemented prototype is robust and successfully performs parking space detection and automatic steering control. Finally, the low cost design and implementation of the PPAS was possible due to the cheap ultrasonic sensors, simple hardware design and low computational complexity of the proposed algorithm.

KEY WORDS : Parallel parking assist, Ultrasonic sensor, Parking space detection, Parking control

1. INTRODUCTION

Recently, the production and sales of vehicles have rapidly increased compared to the expansion of roads and parking spaces. Narrow parking spaces along with these latest trends can cause inconvenience to many drivers. Therefore, intelligent parking assist systems (IPASs) can be helpful to drivers because the IPAS provides information about the parking space, the ideal parking path and automatic steer- ing control. According to J. D. Power’s “2001 Emerging Technology Study”, 66% of consumers indicated that they were likely to purchase intelligent parking assist products (Frank, 2004).

Until now, the development of IPAS has used several types of range and vision sensors. For example, there are IPASs based on camera sensors (Vestri et al., 2005; Jung et al., 2006), ultrasonic sensors (Santonaka et al., 2006), radar sensors (Stefan and Hermann, 2006) and laser sensors (Hirahara and Ikeuchi, 2003). Among these sensors, IPAS development based on ultrasonic sensors is an important issue to reduce the cost of the system. Moreover, it is also important that an IPAS be constructed using ultrasonic sensors as few as possible in a vehicle.

Generally, the IPASs can be classified into parallel park- ing assist systems (PPASs) and cross parking assist systems

(CPASs), which are called garage parking assist systems or perpendicular parking assist systems. In Europe, VALEO’s PPAS, which is called Park4U, uses 10 ultrasonic sensors: 2 side sensors for parking space detection and 4 rear and 4 front sensors for parking assistance (John, 2006).

In this paper, we propose a low cost PPAS using 2 side ultrasonic sensors. After the proposed PPAS finishes detecting the parking space, it can guide the vehicle to the parking destination without the assistance of additional rear or front sensors.

Our proposed PPAS is shown in Figure 1. First, the scanning process for measuring a parking space is perform- ed when the driver gives the start command. In this pro- cess, the PPAS provides information about the surround- ings to drivers in both a graphical and audible format through the human machine interface (HMI) module. In the

[pic 1]

*Corresponding author. e-mail: erjsh@mando.com        Figure 1. Operation procedure of PPAS.[pic 2]

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second step, the driver can stop the vehicle and change the gear position into reverse. In the last step, if the scanned space is large enough for parking, the PPAS guides drivers to the parking destination with the EPS control command. Moreover, the PPAS can provide feedback instructions and emergency stop warnings to drivers through the HMI module until the parking procedure is over.

In this paper, the design process and implementation of this PPAS based on ultrasonic sensors are meant for a low cost design. The proposed PPAS prototype was constructed using only two ultrasonic sensors to reduce the cost. We improved the error rate of vehicle corner detection with the proposed novel sensor design and algorithm. Moreover, the simple hardware and software architecture of the PPAS were implemented. The experimental results demonstrate that the proposed prototype is robust and successfully performs parking space detection and automatic steering control. In the conclusion section, we discuss potential improvements and the direction of our future research.

1. SYSTEM DESCRIPTION

In this section, the configuration and state diagram of the proposed PPAS is described. Figure 2 shows the configu- ration of the PPAS. The PPAS consists of 2 ultrasonic sensors, electric power steering (EPS), electronic stability control (ESC), an electronic control unit (ECU), a HMI, a steering angle sensor (SAS), and a wheel speed sensor (WSS).

The ultrasonic sensor, which is connected to ECU by LIN, performs the search operation for parking space detection. The EPS transfers the steering angle information from the SAS to the ECU and receives the control com- mand from ECU by CAN, and then, it performs steering control operation as an actuator. The ESC, which is con- nected to the WSS, provides wheel pulse data to the ECU to estimate the position of the vehicle. The HMI allows communication between the driver and the PPAS. The ECU, which is connected to the EPS, ESC and HMI, can initialize and communicate with these connected devices and operate the algorithm for parking space detection and parking control.  

[pic 3]

Figure 2. Configuration of PPAS.

[pic 4]

Figure 3. Operation state diagram of PPAS.

[pic 5]

Figure 4. Hardware and software architecture of PPAS.

The operation state diagram of the PPAS is shown in Figure 3. If the driver pushes the system start button on the HMI, the ECU receives the initialization command flag from HMI by CAN, which changes the system into the ready state. The system ready state means that the ECU is turned on and finishes preparing to communicate with each module. After the system reaches the ready state, the park- ing space is measured when the driver indicates that the scan should begin. If there is enough parking space, the PPAS informs drivers about the possible parking space and the best parking path. The starting position and destination

for parallel parking is shown to drivers on the display panel of HMI.

Currently, the driver drives the vehicle to the start posi- tion, until the vehicle stop sign appears on the screen of the HMI, and then puts the vehicle into reverse. After this step, if the driver puts his foot down, the vehicle automatically moves to the parking destination according to the EPS control command of the ECU. If the vehicle arrives at the destination, the PPAS informs the driver that parking is complete and a stop sign appears on the screen of the HMI.

1. SYTEM DESIGN AND IMPLEMENTATION

In this section, the architecture and design process of the proposed PPAS is described. As shown in Figure 4, the PPAS is separated into three parts: the ECU module, SENSOR module and HMI module. The SENSOR module consists of three types of sensors: ultrasonic sensors, WSS connected to ESC and SAS connected to EPS. Ultrasonic sensors are used to classify obstacles and empty space between vehicles after scanning parking space. Then, the WSS and SAS data are used to estimate the vehicle position and range. Lastly, the EPS receives the steering angle com- mand from the ECU module and operates as a controller for steering actuation. The ECU module was designed using a low power 16-bit micro-controller and a simple I/O interface for communication with several peripherals. Further-

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